1. Field of the Invention
This invention relates to a bed warmer such as an electric blanket.
2. Description of Prior Art
In recent years, an electric blanket has widely been used as a bed warmer. In general use of the electric blanket, it is considered to be preferable that pre-heating or preparatory supply of power is effected in advance for about one hour by setting a knob serving as a temperature set means to a scale "high" and subsequently the knob is set to a lower scale of preference when the user goes to bed. Such an operation is always required upon the use of the electric blanket. But the user often goes to sleep while the knob is still set to the "high" scale in the course of the preparatory supply of power, resulting in a problem that due to oppressive heat, the user is forced to wake up.
FIGS. 1a and 1b illustrate a conventional bed warmer in which only a knob is provided for adjustment of a preparatory supply of power. The bed warmer comprises a blanket body 1, a heater conductor 2 wired in the blanket body 1, a controller 3 incorporating a control unit for controlling supply of power to the heater conductor 2 and a power supply circuit, and a temperature control knob 4 mounted in the controller 3.
FIGS. 2 shows a temperature characteristic when the electric blanket is in use. A temperature response illustrated in FIG. 2 is obtained by initially setting the knob to a scale "high" at a time a so as to effect preparatory supply of power for about one hour and subsequently setting the knob to a scale of preference at a time b at which the user goes to bed.